The invention is a method of repairing multiple tube structures, more particularly an in situ method of repairing multiple tube sign supporting structures, including multiple aluminum tube sign supporting structures.
Across the United States, there are thousands of highway sign structures, with tens of thousands of weld joints. Some of which extend across as many as 10 lanes of traffic. In many of these structures, two to four elongate larger header tubes are welded together in a framework with a number of smaller cross-member tubes, which cross-member tubes are frequently attached in an angled relationship, to create many generally triangular sections. However, sign structures can take other forms of multiple tubes welded together. Since there are a great number of different shapes, angles and sizes of joint members, construction of prefabricated reinforcement clamps is not always practical. A large number of these structures are upwards of 30 and 40 years old and have been exposed to as many years of harsh conditions such as freezing winters and ice buildup, hot summers, high winds and storms and other vibration loads, and the corrosive effects of acid rain and salt laden air. One main cause for cracking of the welds is that the welds were not made properly in the first place. Sometimes, the welds have very poor penetration and were not done with the structure preheated. Also, the aluminum in the area of the welds may have been annealed during the weld process and the structure was not reheat treated to the T6 condition. There is also evidence of internal strains in some of the structures caused by improper alignment of the pieces that are welded together. There is also evidence that the entire structure is subjected to stress when they are installed, and there are cases of the entire structures being twisted and bent. Repair by welding over traffic can be difficult to accomplish. The cost to replace these structures is extremely high, and known methods to repair such sign structures in situ are expensive, time consuming, and impractical.
There accordingly remains a need for a new method for in situ repairing of tubular sign supporting structures which is cost effective, quick, and practical.
The method of the invention for making on site repairs of structures having welded together sections of elongate members, such as tubular headers (or chords) and struts and involves the following basic steps. First, pilot holes are preferably drilled slightly beyond the ends of any weld cracks in the sound region of the weld metal to relieve stress and prevent the crack propagation. If the weld is cracked all the way around or nearly all the way around, this drilling step can be skipped. Next, the structure is cleaned in the vicinity of the repair site. This can be done by using a combination of a caustic cleaner scrub followed by water rinse and then followed by an acid etch scrub and a water rinse. After this, the surfaces are mechanically roughed up (e.g. with emery cloth, a file, sandblasting, or other known methods) and then are acid-etched and rinsed once again, followed by clean towel and then air drying. Other cleaning and surface preparation steps can also be used, such as combinations of mechanical abrasion and chemical washes. Next, a filler coving (e.g. an epoxy putty) is applied to the tube joints at any acute angle areas and/or at areas with sharp joints to flatten out the tight angled areas. This flattening out is helpful in that it ensures close bonding of wrap layers to the structure (described below). After a brief curing period, a chrome conversion coatings for aluminum is used to treat the tubes. Next, the tubes and filler are rinsed and air-dried. Next, a primer, for example, a urethane resin, is applied to the tube surface and to the putty and is allowed to tack up. Following this, a fiber wrap (e.g. fiberglass) pre-impregnated with a resin (e.g. a water cured urethane resin), such as Air Logistics Corporation""s Aquawrap(copyright) Type G-03 xe2x80x9ctapexe2x80x9d product, is water wetted and is wrapped around the smaller cross-member tubes in a helical bandage wrapping method to create a relatively smooth and flat composite layer. Depending upon the application, the header tubes can also be wrapped with helical bandage wrapping as well. Typically, it is desirable for this first wrapping material to be of a fine weave (light-weight tow), so that the maximum contact is achieved between the reinforcing fiber and the bonding surface(s). Next, saddle segments of fiberglass water cured urethane resin pre-preg are placed on the header tube and cross-member tubes in the areas of any acute angles where the header tube and cross-member tubes are joined and the wrap segments are positioned so they lay down smoothly against all surfaces including against the filler used to reduce the sharpness of the joint regions. Next, saddle segments of fiberglass water cured urethane resin pre-preg are placed on the cross-member tube and header tube in their obtuse angle regions. Following this, elongate and narrower but thicker, uni-directional fiber xe2x80x9ctendonxe2x80x9d pre-pregged segments are laid down on one side face (e.g. the left side face) of the smaller cross-member tube, cross under the larger header tube, and continue to wrap to the other side face (e.g. the right side face) of the smaller cross-member tube. The process is repeated with another tendon segment on the other sides of the smaller tubes. Following this, the tendon segments are secured to the smaller tubes by helical wrapping with more of the tape pre-preg. Next, two additional saddle segments of the fiberglass water cured urethane resin wraps are placed on the header tube and cross-member tubes in the areas of the acute angles and are positioned so they lay down smoothly over the previously installed wrap. Following this, additional saddle segments of the fiberglass water cured urethane resin wraps are used in their obtuse angle region. Starting at the joint crotches, the tape pre-preg is used to completely encapsulate all of the composite layup components. Next, the repair site is tightly wrapped by Air Logistics Stricture Banding(trademark), preferably in the same wrap direction as the fiberglass water cured urethane resin wraps. When stretched, as it is being wrapped, through its elastic properties, the Stricture Banding(trademark) tightly compresses the layup against the tubes and putty. Due to the geometry of tubular intersections, there are some spots, most particularly in the deepest crotch of the welds in the most acute angles, where the Stricture Banding(trademark) would not normally impart enough compressive force down onto the layup. To ensure that the layup tightly seats around the weld joints in these problem areas, a load transfer xe2x80x9crodxe2x80x9d, most desirably a closed cell poly foam extruded shape (often called xe2x80x9cbacker rodxe2x80x9d in the trades) can be seated around and over the problem areas. Then by overwrapping this load transfer rod with Stricture Banding(trademark), the Stricture""s load is conveyed from an area where it can be effected (the outside diameter or edge of the load transfer rod) to the area where the load is needed (the crotch of the weld, for instance). Aquawrap(copyright) products evolve a small amount of carbon dioxide gas when they cure. Because the evolution of this gas can become entrapped beneath the Stricture Banding(trademark), the Stricture Banding(trademark) can preferably be ventilated by poking holes in it, using the point of a sharp knife or a perforating roller, known in the trade as a xe2x80x9cporcupine rollerxe2x80x9d. This permits curing bubbles and any excess water to escape. The repair is allowed to cure for the required amount of time, e.g. 30 minutes or until hardened. The Stricture Banding(trademark) and backer rod are unwrapped and/or removed, the composite repair site is permitted to air dry. The repair site can then be painted if desired.